There is, for example, a conventional method disclosed in JP-A 53-12842 in which 2-alkyl-3-oxo-cycloalkyl dimalonate is reacted with water having an amount of 1 to 1.5 mol equivalents to the diester at 200 to 260° C. under atmospheric pressure, as a method of producing an acetate derivative by supplying water to a 2-alkyl-3-oxo-cycloalkyl dimalonate to run demonocarboxylation. JP-A 9-183754 discloses a method in which a 2-alkyl-3-oxo-cycloalkyl dimalonate is reacted with water having an amount of 1 to 3 mol equivalents to the diester at 150 to 250° C. JP-A 56-147740 discloses a method in which a 2-alkyl-3-oxo-cycloalkyl dimalonate is reacted with water at 180 to 210° C. under 1 to 10 atmospheric pressures.